# invoices.setProject

Tie up to 100 invoices to a project (a project tag's id from tags.list) or clear it with projectId null. Works on issued invoices too, because the project is internal and never printed. Archived projects can't be chosen. Returns the invoices changed and any left alone.

`POST /api/v1/accounting/invoices.setProject`

Permissions: `accounting:read`, `accounting:write` · Roles: admin, finance · Idempotency key required

MCP tool: `accounting_invoices_set_project`

## Fields

| Field | Type | Required | Notes |
| --- | --- | --- | --- |
| `ids` | array of strings (ID) | Yes | 1–100 items. |
| `projectId` | string (ID) or null | Yes |  |
| `idempotencyKey` | string | Yes | Any unique text you generate once per intended change, so a retried request only happens once. Send it as the Idempotency-Key header instead if you prefer; if you send both they must match. 8–200 characters. |

## Example request

```bash
curl https://app.getoatmilk.com/api/v1/accounting/invoices.setProject \
  -H "Authorization: Bearer $OATMILK_API_KEY" \
  -H "Content-Type: application/json" \
  -H "Idempotency-Key: $(uuidgen)" \
  -d '{
  "ids": [
    "9a8b7c6d-5e4f-4a3b-8c2d-1e0f9a8b7c6d"
  ],
  "projectId": "4d5e6f7a-8b9c-4d0e-8f1a-2b3c4d5e6f7a"
}'
```

Reference page: https://app.getoatmilk.com/docs/api/invoices.setProject